Flies helping control region's winter moths

Saturday

May 10, 2014 at 12:01 AM

By Scott O'ConnellDaily News Staff

SHERBORN - It may be difficult to think of the fly as a conquering hero. Yet in the ecological battle being waged in the region's treetops right now, the tiny nuisance is proving to be just that.On Friday, UMass Amherst professor Joseph Elkinton released 2,000 of the insects, which are of a European variety known as Cyzenis albicans, at the Rocky Narrows reservation, where the hope is the flies will feed on their favorite prey, the winter moth caterpillar.The ravenous winter moth, which has been in Massachusetts for just over a decade, has decimated the state's trees, which the inchworm-like caterpillars nibble away at until the plant dies of exhaustion trying to replace its tattered leaves. While sprays have had minimal effectiveness controlling the moths, Elkinton and local arborists think they have a permanent solution with the fly, which has been successful in reducing winter moth populations in areas where they've been introduced.At Centennial Park in Wellesley, for instance, where the flies were released in 2008, the moths' numbers are just 5 percent of what they were a few years ago."That's a dramatic difference," said Rolf Briggs, consulting arborist at Tree Specialists, Inc. in Holliston, who added that the reduction has led to a rebound by the park's trees, which had been "absolutely defoliated.""The exciting thing is we know (the flies) are successful in the region," Briggs said. "That's a big relief."If the flies hadn't worked out, it would have been a significant blow to Elkinton and his team at UMass, who have spent years meticulously raising thousands of the insects, which only have a couple generations per year and are thus difficult to take care of in captivity. On several occasions, they had their $150,000 annual state funding cut, but each time were able to muster enough political favor to get it back, Briggs said.Elkinton is confident the flies also won't cause problems of their own."It's an absolute specialist on winter moths," he said. "It won't move on to other kinds of moths and butterflies. As the density of the winter moths decline, the flies' density will decline as well."In a gruesome example of parasitism, the flies essentially incubate inside the moths after their eggs, which they deposit on the leaves of tree species favored by the winter moth, are consumed by the caterpillars. The moth then dies during its pupa phase, and an adult fly emerges from its cocoon instead.It takes several years for the fly population to establish itself, but once it does, Briggs said the hope is the insects will eventually spread beyond the area where they are introduced. That would be good news for residents of Sherborn, where the winter moth has become a ubiquitous pest in recent years."People get (the adult moths) all around their doorways, and let them in by mistake. They don't harm anything, but they're freaky," Briggs said, adding the moths strike an especially eerie scene when they congregate in massive numbers at the intersection of routes 27 and 16 in the late fall. "The place looks like something from Alfred Hitchcock."After wrapping up at Rocky Narrows Friday morning, Elkinton said he planned to do another release later that afternoon at Holts Grove in Marlborough."You try to stagger them around Massachusetts," said Briggs, who added Elkinton has permission to introduce the flies at Wellesley College, for example, but is holding off because of the campus's proximity to Centennial Park.Elkinton said he expects to have around 30,000 of the insects ready to go this year."We have to nurture them for a whole year before we can release them," he said. "Slowly but surely, we've honed our technique."Scott O'Connell can be reached at 508-626-4449 or soconnell@wickedlocal.com. Follow him on Twitter: @ScottOConnellMW